The present invention relates to an oil filter unit, which is disposed in an oil collection chamber, such as an oil pan or a housing. Oil filter units of this type are used, for example, to filter the lubricating oil of gears, e.g., automatic transmissions. To adapt the filter unit to the space available for installation, it is designed in the shape of a pan and can be positioned directly within the oil sump. The purpose is to separate impurities from the lubricating oil and thereby to increase the life of the lubricating oil and minimize the wear of the unit to be lubricated. The oil filter unit should have the greatest possible filter fineness and minimum flow resistance and at the same time adequate dirt holding capacity and, in motor vehicles with automatic transmissions, should be designed to last for the life of the vehicle.
Published US patent application no. US 2002/0121473 A1 (=EP 1,238,693) discloses an oil filter assembly having a filter chamber in a pan-shaped housing, which communicates with an oil inlet and an oil outlet. A replaceable filter element supported by ribs is disposed inside the filter chamber. The hollow filter element is spatially substantially parallel to the filter chamber, such that the fluid flows from the outside toward the inside.
A disadvantage of this design is that because of its replaceability, the replaceable filter element must have a complex seal relative to the housing at its opposite end faces. This seal requires corresponding contours on the filter element and the housing, which enable a releasable yet fluid-tight connection. Producing these contours places high demands on the manufacturing process. Furthermore, the size of the filter surface depends directly on the circumference of the filter chamber, which implies a substantial restriction with regard to the adjustment between dirt holding capacity and filter fineness. Because of this restriction, the described oil filter assembly cannot be used with a filter medium that ensures the filter fineness required for the operation of automatic transmissions. Use of such a filter medium would exceed the pressure differential required in suction operation. To meet this requirement in practice, a coarse particle filter is used on the inlet side and an additional fine particle filter downstream of the coarse filter is used on the pressure side.